1. Field of the Invention
The present invention relates to a shaft drive type motorcycle having a drive shaft.
2. Description of Background Art
A shaft drive type motorcycle is known wherein a drive shaft is provided on the lower side of a pivot shaft, and a driving force of an engine is transmitted to a rear wheel by the drive shaft. See, for example, Japanese Patent Laid-open No. 2008-87540 (FIG. 3).
In FIG. 3 of Japanese Patent Laid-open No. 2008-87540, a swing arm 12 (the reference symbols used in the document are used as they are here) swingably supports a rear wheel 2 (the swing arm will hereinafter be referred to as “the swing arm 12”) is provided on the left side in the vehicle with a gear box 44 being provided at a rear part of the swing arm 12. A drive shaft 45 for transmitting the motive power of an engine to the rear wheel 2 is provided on the inner side of the swing arm 12 with a drive axle 56 (hereinafter referred to as “the rear wheel axle 56”) penetrating the inside of the gear box 44. The rear wheel 2 is mounted to the rear wheel axle 56.
In the technology described in Japanese Patent Laid-open No. 2008-87540, a brake disc 15 is laid on the rear wheel axle 56 with a hub 55 of the rear wheel 2 being laid on the brake disc 15. Nuts 58 . . . ( . . . means plurality, here and hereinafter) are fastened to bolts 57 . . . erectly provided on the rear wheel axle 56, from the outer side of the hub 55. In other words, the rear disc plate 15 is co-fastened to the rear wheel axle 56 together with the hub 55, by the bolts 57 . . . and the nuts 58 . . . .
The brake disc 15 configured as described above is formed to have a predetermined plate thickness as measured outwards from the fastening positions of the bolts and the nuts. In the brake disc 15, the inside part not sandwiched by a rear brake disc caliper does not exhibit the function intrinsic of the brake disc 15. Therefore, there is room for improvements from the viewpoint of reducing the vehicle weight.
Though not disclosed in Japanese Patent Laid-open No. 2008-87540, the inside of the gear box 44 is filled with lubricating oil, and an oil seal is provided between the gear box 44 and the rear wheel axle 56. Further, for making it difficult for the oil to leak, a labyrinth plate having a labyrinth structure or the like member is provided in addition to the oil seal, so as to contrive an enhancement of the oil sealing performance and for prevention of mud, water or the like from coming in from the outside.
In the above-mentioned structure, however, the labyrinth plate having a labyrinth structure or the like member is needed as a separate component part. Accordingly, the number of component parts is increased, which may lead to an increase in the vehicle cost.